Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in the United States of America, or elsewhere, on or before the priority date of the disclosure herein.
Australian/New Zealand Standard (“AS/NZS”) 3500.3:2015 (hereinafter simply referred to as “3500.3”) stormwater drainage code (titled Plumbing and drainage Part 3 Stormwater drainage) specifies three types of overflow devices for box gutters, namely: (a) a rainhead; (b) a sump/side overflow device; and, (c) a sump/high capacity overflow device.
A rainhead operates in such a manner that an increase in the depth of water flow in a box gutter, operating up to its maximum design hydraulic capacity, is not required when the downpipe becomes blocked and the stormwater is required to overflow a wall forming a weir at the front of the rainhead and discharge to atmosphere. Conversely, types (b) and (c) above do require an increase in the depth of flow in the box gutter when the downpipe is blocked, in order for the device to allow overflow to occur up to the maximum design hydraulic capacity of the box gutter.
This invention relates to the first of the three types of above noted overflow devices, namely (a), and may be an alternative to the rainhead as currently prescribed by 3500.3.
The proposed invention may operate in a similar manner to the currently prescribed rainhead in that, under normal flow conditions up to the design hydraulic capacity of the box gutter, the stormwater discharges into the downpipe connected to the underside of the rainhead, and from there flows in an unimpeded manner to the legal point of discharge for the property via the underground stormwater drains. However, this invention differs significantly from the currently prescribed rainhead in the following manners:                a) This invention is physically similar to the prescribed rainhead, except that it has an additional external ‘compartment’ at the front of the rainhead, which hides the weir, effectively making this an ‘internal’, non-visible, weir.        b) When the downpipe is blocked or its flow capacity is exceeded, instead of the stormwater overflowing an ‘external’, visible weir and discharging directly to the atmosphere as drawn in 3500.3, the stormwater firstly overflows the (now) ‘internal’, non-visible weir, and then potentially impacts with the ‘external tub wall’ (outer wall of the additional external compartment), before finally discharging vertically, or near vertically, to atmosphere through the primary overflow outlet at the bottom of the rainhead.        c) This invention has a secondary overflow provision, being an outlet/opening (typically rectangular, but other shapes, such as circular may be used provided they supply the necessary capacity) located within the front face of the device (the external tub wall), which operates in a similar manner to the overflow for a sump/side overflow device. However, it is considered extremely unlikely that this secondary overflow provision would ever be required, since it would require both the downpipe/internal receptacle and the ‘primary’ overflow provision to both be blocked.        d) This invention is considered to have a significant aesthetic advantage over the currently 3500.3 prescribed rainhead because the additional compartment at the front of the device effectively hides the box gutter and the weir, albeit other than a small portion of which may be visible through the secondary overflow provision. It is therefore considered to be a substantially visually preferable device, which is significantly more likely to be selected by architects, building designers and plumbers and the like, over the currently prescribed rainhead in 3500.3 (which in itself is not even commercially available).        
This invention is also considered to have substantial advantages over the prior art because visual inspection from below (typically at ground level), and even by a completely untrained person, can quickly and easily confirm if the primary overflow outlet is blocked or clear. The design of the invention ensures that as long as the primary overflow remains visually clear, the invention will continue to work and protect the building from internal flooding. This is unlike currently available rainheads, all of which require access to the rainhead itself (or above it) for inspection purposes. The invention therefore has substantial Occupational Health and Safety benefits in association with routine maintenance and inspections.